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Apache Log4j2 Deserialization of Untrusted Data Vulnerability

Exploited · KEV 2023-05-01RansomwareMetasploit moduleCVE-2021-45046CWE-917

Exploited since 2023-05-01. 2 of 8 rule sources name it. Our CRS test: blocked.

Edge rules
2/8
Our test
Blocked
CVSS
9.0
EPSS
100.0% Top 0.1%
Posts, 14d
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Published
2021-12-14
It was found that the fix to address CVE-2021-44228 in Apache Log4j 2.15.0 was incomplete in certain non-default configurations. This could allows attackers with control over Thread Context Map (MDC) input data when the logging… More

It was found that the fix to address CVE-2021-44228 in Apache Log4j 2.15.0 was incomplete in certain non-default configurations. This could allows attackers with control over Thread Context Map (MDC) input data when the logging configuration uses a non-default Pattern Layout with either a Context Lookup (for example, $${ctx:loginId}) or a Thread Context Map pattern (%X, %mdc, or %MDC) to craft malicious input data using a JNDI Lookup pattern resulting in an information leak and remote code execution in some environments and local code execution in all environments. Log4j 2.16.0 (Java 8) and 2.12.2 (Java 7) fix this issue by removing support for message lookup patterns and disabling JNDI functionality by default.

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Ask about CVE-2021-45046: who's covered, what to patch first, how vendors compare. I cite sources and won't help with attacks.

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Severity, decoded

CVSS 3.1
Critical · 9.0 / 10

Exploitable over the network under specific conditions, with no privileges and no user interaction, leading to full loss of confidentiality, integrity and availability, and the impact can reach components beyond the vulnerable one.

Over the internetNo login neededNo user actionHard to pull offSpreads beyond the appFull compromise
How the score is built8 metrics
  • Attack vectorAn attacker can reach it over the internet; no access to your network needed.
    Network
  • Attack complexityThe attack only works when conditions outside the attacker's control line up.
    High
  • Privileges requiredNo account or login is needed.
    None
  • User interactionNo one has to click or open anything; the attack works on its own.
    None
  • ScopeThe attack can spread beyond the vulnerable component to other parts of the system.
    Changed
  • Confidentiality impactAn attacker can read all data the affected component holds, or the most sensitive parts of it.
    High
  • Integrity impactAn attacker can change any data or files the affected component protects.
    High
  • Availability impactAn attacker can take the component down completely or keep it from serving anyone.
    High
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
CISA's assessmentSSVC, from the CVE record
ExploitationActive

Attackers are exploiting this in the wild.

AutomatableNo

At least one step needs hands-on work, which slows mass attacks.

Technical impactTotal

A successful attack gives full control over the affected software or all of its data.

Public exploits

2 found
1 Metasploit0 Exploit-DB1 Scanner template0 GitHub PoCs

Links are to third-party code: never run it outside an isolated lab.

Timeline

  1. 2021-12-09
    Metasploit module published
    Log4Shell HTTP Scanner
  2. 2021-12-14
    CVE published
    CVE List
  3. 2023-05-01
    Added to CISA KEV
    Confirmed exploitation in the wild
  4. 2026-11-02
    Our test: OWASP Core Rule Set blocked it
    paranoia level 1, anomaly threshold 5, default CRS settings
  5. 2026-11-02
    Our test: OWASP Core Rule Set blocked it
    paranoia level 2, anomaly threshold 5, default CRS settings

Social

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No posts seen yet on X, Bluesky, Mastodon, Hacker News or GitHub.

Vendor statements

Quoted
CloudflareWAF Managed RulesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

AWSAWS WAF Managed RulesNo public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. AWS often describes a vulnerability without naming its CVE (for example "Log4j"). We count only entries that name the CVE, so AWS coverage is understated.

Microsoft AzureFront Door and Application Gateway WAF (DRS)2 quotesRule published
UndatedListed944240Source
Rule 944240: Critical - 5 · 2 · Remote Command Execution: Java serialization and Log4j vulnerability (CVE-2021-44228, CVE-2021-45046)
UndatedListed800100Source
Rule 800100: Critical - 5 · PL2 · Rule to help detect and mitigate log4j vulnerability CVE-2021-44228, CVE-2021-45046
Google CloudCloud Armor preconfigured WAF rules1 quoteRule published
UndatedListed…4228-cveSource
Signature owasp-crs-v030001-id044228-cve (sensitivity 1): Base rule to help detect exploit attempts of CVE-2021-44228 & CVE-2021-45046
FastlyNext-Gen WAF virtual patchesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

F5Attack signatures (Distributed Cloud WAF)Before feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

AkamaiApp & API Protector (Adaptive Security Engine)No public source

This vendor publishes no machine-readable rule changelog we can check.

OWASP CRSCore Rule Set (open source, used inside many WAFs)Before feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.